Stress

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Abstract

In North-western Europe, with the holiday season safely behind us, daily laboratory routine is back, and with a concept we use on an almost daily basis, but rarely ever think about: stress. The everyday use of the term itself has a rather interesting history, from material science to a negatively connoted disruption of homeostasis to a defining feature of the successful young professional in the 21st century. Let’s take a look from the physiologist’s perspective: In physics, stress is a physical quantity. It describes the forces which adjacent particles within a continuous material exert on each other – not, and this is important, the reaction of the material to these forces – in physics, that would be strain. Stress as a technical term entered the life science community in 1926, when Walter B. Cannon (1871– 1945) used it for the entirety of external factors disrupting homeostasis of a living organism (Cannon 1926). From there, the concept rapidly developed: Hans Selye (1907–1982) used ‘stress’ in a biological context to describe ‘the non-specific response of the body to any demand placed upon it’. Selye’s GAS concept describes the phaseal stress response: sympathetic nervous system activation and non-specific mobilization, followed by a coping/resistance phase and, if homeostatic disruption fails to subside and resources are depleted, exhaustion (Viner 1999). Cause and effect become confused. Selye itself recognized the ambiguity: In James Humphrey’s ‘Anthology of Stress Revisited’, Paul Rosch describes how, ‘in helping him [Hans Selye] to prepare his First Annual Report on Stress 1951, I included the comments of one physician published in the British Medical Journal, who, using citations from Selye’s articles, concluded that “Stress, in addition to being itself, was also the cause of itself, and the result of itself”’ (Humphrey 2005). Utilizing stress as a search term in a biomedical database impressively demonstrates the slippery quality of the term ‘stress’ somewhere between physics, physiology and psychology, somehow denoting both cause and effect. Many excellent publications in Acta Physiologica colourfully illustrate the wide spectrum of physiological stress research: As shown above, the study of physiological mechanisms involved in stress-related psychological reactions at one end of the spectrum and, at the other, physical effects such as changes in blood flow and thus altered shear stress conditions on the vascular wall are major interests of modern-day physiologists (Banfi & Gianni-Barrera 2015, Uchida et al. 2015). Stressed podocytes, admittedly, came as a surprising concept: Golubinskaya and colleagues recently looked into the regulation and putative function of calcium-activated chloride channels, namely bestrophins, under conditions of endoplasmic reticulum stress (ER stress) induced by lipopolysaccharide exposure of renal podocytes (Golubinskaya et al. 2015, Svenningsen 2015). In physiology, ‘classical’ disturbances of homeostasis occur in the form of, for example aberrations in temperature (Ohno et al. 2015), tissue oxygen tension (Bailey et al. 2014, Iversen et al. 2014, Chytilov a et al. 2015, Heimlich et al. 2015, Nikpour et al. 2015) or metabolic substrate concentration (Mapanga et al. 2014). Oxidative stress is a major focus of physiological and pathophysiological studies (Heinonen et al. 2014, Konstantinidis et al. 2014, Usui et al. 2014, Persson et al. 2015, Zuo et al. 2015a,b). As a necessary survival response, stress is widely conserved across the vertebrate species (Tasker & Jo€els 2015). The global stress response gears us up for fight or flight. However, even in these modern days we cannot outrun biology and the stress response often backfires due to our sedentary lives. It is simply not advisable to attack your boss or do a 100-m dash across the institute as soon as one feels pressured by the colleagues during a meeting. This back-firing of our biological system vs. our work life may results in stress-related illness, which is estimated to have the cost EU 61.7 billion EUR in 2014 alone (EU-OSHA, 2015). The concept of stress is hard to grasp, while at the same time, almost every layperson at any given cocktail party probably feels enabled to give a valid definition. Both physiologists and psychologists have struggled for a valid and concise definition, a current one, convincing in its simplicity, being ‘conditions where an environmental demand exceeds the natural regulatory capacity of an organism’ (Koolhaas et al. 2011). Acute and chronic stress differ (e.g. Schneiderman et al. 2005). During the acute stress response, a threat is identified and the body initiates a chain reaction of events to maximize muscular output and reaction